What's Wrong With My Code? A Troubleshooting Guide for Junior Developers

Introduction: The Debugging Mindset

If you're reading this, you're likely frustrated. You've stared at the same block of code for an hour. You've questioned your career choice.

Take a breath.

Debugging is not failure; it's the job. Senior developers don't write perfect code; they just spot errors faster. The difference between a Junior and a Senior dev isn't avoiding bugs—it's having a systematic process to kill them. This guide is that process.

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Part 1: Common Code Error Types (The "Big Three")

Before you fix it, you must name it. Errors generally fall into three buckets.

| Error Type | What It Means | Symptoms | Difficulty to Fix | |------------|---------------|----------|-------------------| | Syntax Error | Grammar mistake. You broke the language rules. | The code won't run at all. Red squiggly lines in your IDE. | Easy (1/5) | | Runtime Error | The code runs, but crashes midway. | App freezes, "Exception" messages, or sudden shutdown. | Medium (3/5) | | Logic Error | The code runs perfectly, but does the wrong thing. | Incorrect math results, loops that never end, wrong data displayed. | Hard (5/5) |

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Part 2: The Systematic Debugging Process

Stop randomly changing variables hoping it works. Use the R.L.U.I.T. method.

Step 1: Read the Error Message (Actually Read It)

Most juniors gloss over the red text. The error message usually tells you the exact line number.

• Bad: "It's broken."
• Good: "Uncaught TypeError: Cannot read property 'map' of undefined at line 42."

Step 2: Locate the "Scene of the Crime"

Go to the line number mentioned. If the error is "undefined," look at where that data comes from (usually the lines before).

Step 3: Explain the Code Out Loud (Rubber Ducking)

Explain what your code should do, line-by-line, to an inanimate object (or a colleague). You'll often catch the logic flaw simply by vocalizing it.

Step 4: Isolate the Variable

Comment out unrelated code. Run only the specific function causing the crash. If it works, the bug is elsewhere.

Step 5: Test and Verify

Once fixed, try to break it again. Does it handle edge cases (e.g., empty lists, zero values, null inputs)?

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Part 3: Language-Specific Troubleshooting

We've categorized common pitfalls by language.

1. JavaScript: The "Undefined" Nightmare

The Symptom: Uncaught TypeError: Cannot read properties of undefined The Cause: You're trying to access a property of an object that doesn't exist yet (likely due to an async API call).

❌ Broken Code:

const user = await fetchUser();
console.log(user.profile.name); // Crashes if user is null

✅ Fixed Code (Optional Chaining):

const user = await fetchUser();
console.log(user?.profile?.name); // Returns undefined instead of crashing

2. Python: The Indentation Trap

The Symptom: IndentationError: unexpected indent The Cause: Mixing tabs and spaces. Python is strict about whitespace.

❌ Broken Code:

def calculate_total(items):
  total = 0
    for item in items: # Extra space here causes crash
      total += item
  return total

✅ Fixed Code:

def calculate_total(items):
    total = 0
    for item in items: # Aligned correctly
        total += item
    return total

3. SQL: The Silent Empty Result

The Symptom: No error message, but no data returns. The Cause: Usually a JOIN issue or case sensitivity.

❌ Broken Code:

SELECT * FROM users WHERE email = 'User@Example.com'; -- Fails if DB is case sensitive

✅ Fixed Code:

SELECT * FROM users WHERE LOWER(email) = 'user@example.com';

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Part 4: Tools That Save Your Sanity

Don't debug with just your eyes. Use tools.

1. Browser DevTools (F12): Essential for web devs. Use the "Network" tab to see if your API request actually fired.
2. Linters (ESLint / PyLint): These are spellcheckers for code. They catch syntax errors before you run the app.
3. FlowQL (The Expert Layer): Sometimes, tools aren't enough. When you've spent 2+ hours on a bug, you need a human eye. FlowQL allows you to post your specific snippet and get annotated fixes from vetted senior engineers, not just generic AI answers.

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Part 5: When to Ask for Expert Help (The 2-Hour Rule)

If you've been stuck on the same bug for 120 minutes, stop. You have tunnel vision.

How to ask for help effectively:

1. Context: "I'm trying to do X, but Y is happening."
2. Evidence: "Here's the error log and the specific code block."
3. Attempts: "I've already tried A, B, and C."

Pro Tip: Don't paste 500 lines of code. Paste the 10 lines that matter.

Why FlowQL? Unlike Stack Overflow, where you might get downvoted for a "duplicate question," or ChatGPT, which might hallucinate a library that doesn't exist, FlowQL connects you with verified experts who debug for a living. It's the "Senior Dev" you wish sat next to you.

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Conclusion: Building Debugging Resilience

Every error you fix adds to your mental library. The Senior Developer who solves the bug in 5 minutes does so because they spent 5 hours solving it ten years ago.

Your Next Step: Keep this debugging process handy. Next time the red text appears, don't panic—process it.

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FAQ: Common Debugging Questions

Q: Is there an AI that can fix my code? A: Yes, tools like GitHub Copilot and ChatGPT can suggest fixes, but they often struggle with complex logic or context-specific bugs. Always verify AI code before pushing to production.

Q: How do I know if my code is efficient? A: "Working" code isn't always "good" code. Use Big O notation to measure complexity. If your code has nested loops (loops inside loops), it may be slow with large data sets.

Q: Why does my code work on my machine but not on the server? A: This is usually an "Environment" issue. Check your .env variables, file paths (Windows uses \ while Linux uses /), and dependency versions.